Best answer: Check for style and tone.
Taking an assessment of the style and tone of your essay is part of the revision process. The other items mentioned in the list are part of the preparation process or writing process. In the research phase, you are searching for facts and evidence that will go into your essay. In the planning phase, you will establish a thesis and outline of your argument. Then in the writing phase, you will put that clear argument into writing. Once you have written your overall argument, then you would seek to write a strong conclusion to the essay (still in the writing phase). Matters such as proofreading, checking the accuracy of your citations and bibliography list, and checking your style and tone -- those are parts of the revision phase of your essay work.